An adage used as a psychological tool to expose bias.
The key portion is the last word, which used in this context can be interpreted either as a statement of truth (i.e. oranges are
orange) or as a pejorative insult (Those shoes are
gay). Essentially it will trigger people who are easily
triggered. The point of doing this is to show that an inherently unbiased statement is interpreted by the individual to follow their own rationale, often time exposing their bias towards negative interpretation.
Similar to "It's okay to be white".
heilhonkler tweets: "Gay people are
gay."
rando tweets: "@Twitter why do you continue to
allow homophobic hate speech on your platform? People like this are despicable and should be banned."
*outrage ensues*